Hand-held and hand-operated printing devices with an ink-jet print head are known through various documents.
U.S. Pat. No. 5,927,872 by Yamada discloses a system and a method of printing an image represented by a frame of image data utilizing a hand-held printer having optical sensor means for tracking positions of the hand-held printer relative to the surface of a print medium during a printing process. It is monitored in real time using navigation information generated by the optical sensor.
Each optical sensor comprises an array of opto-electronic elements to capture images of the surface of a print medium at fixed time intervals. Preferably, the optical sensor means can detect slight pattern variations on the print medium, such as paper fibers or illumination pattern formed by highly reflective surface features and shadowed areas between raised surface features. These features can then be used as references for determining the position and the relative movement of the hand-held printer. During the printing process, the hand-held printer can also use the printed portions of the image as reference positions.
In the preferred embodiment, the hand-held printer contains a navigation processor and a printer driver. Using the printer driver, the navigation processor drives the hand-held printer to print segments of the image onto a print medium as the hand-held printer travels across the print medium during a printing process. Each segment of the image is printed onto a particular location on the print medium to form a composite of the image.
In the U.S. Pat. No. 6,233,368 B1 by Badyal et al it is taught a CMOS digital integrated circuit (IC) chip on which an image is captured, digitized, and then processed on-chip in substantially the digital domain.
A preferred embodiment comprises imaging circuitry including a photo cell array for capturing an image and generating a representative analog signal, conversion circuitry including an n-bit successive approximation register (SAR) analog-to-digital converter for converting the analog signal to a corresponding digital signal, filter circuitry including a spatial filter for edge and contrast enhancement of the corresponding image, compression circuitry for reducing the digital signal storage needs, correlation circuitry for processing the digital signal to generate a result surface on which a minima resides representing a best fit image displacement between the captured image and previous images, interpolation circuitry for mapping the result surface into x- and y-coordinates, and an interface with a device using the chip, such as a hand-held scanner.
The filter circuitry, the compression circuitry, the correlation circuitry and the interpolation circuitry are all embodied in an on-chip digital signal processor (DSP). The DSP embodiment allows precise algorithmic processing of the digitized signal with almost infinite hold time, depending on storage capability. The corresponding mathematical computations are thus no longer subject to the vagaries of CMOS chip structure processing analog signals.
Parameters may also be programmed into the DSP's software making the chip tunable, as well as flexible and adaptable for different applications.
U.S. Pat. No. 5,644,139 by Allen et al discloses a scanning device and a method for forming a scanned electronic image including the use of navigation information that is acquired along with image data, and then rectifying the image data based upon the navigation and image information. The navigation information is obtained in frames. The differences between consecutive frames are detected and accumulated, and this accumulated displacement value is representative of a position of the scanning device relative to a reference. The image data is then positioned-tagged using the position data obtained from the accumulated displacement value. To avoid the accumulation of errors, the accumulated displacement value obtained from consecutive frames is updated by comparing a current frame with a much earlier frame stored in memory and using the resulting difference as the displacement from the earlier frame. These larger displacement steps are then accumulated to determine the relative position of the scanning device.
The above documents do only teach how to determine the position in a conceptual generation of navigation information. In this context the U.S. Pat. No. 5,927,872 by Yamada uses the navigation information for a hand-held scanner disclosed in U.S. Pat. No. 5,644,139 by Allen et al. The invention according to Allen et al teaches navigation through comparison of pixels on a frame basis.
A disadvantage with the current handheld printing devices originates from the inaccuracy of the printer-sensors providing positional information to the device as to its positioning on a printing medium. The type of position reading sensors currently utilized in such handheld and hand-operated printing devices have a deviation in accuracy for positioning data of about 0.5-1%, consequentially reducing the quality of image printing since a positional divergence of that magnitude is enough for providing either an overlap or a gap between two subsequently printed sections of an image having sides interfacing each other. The complete image printed in sections utilizing printer-positional information as provided by such sensors will in some intersections therefore be either darkened due to overlapping in part of printed image sections or lightened due to a distancing between the same and the total image impression will thus be considerably impaired.
There is always the possibility that a hand-held printing device at occasions is positioned correctly for a subsequent sectional printout of an image, but this is achieved more by chance and not so much by exact positioning through sensor information.
Accordingly, the lack of predictability for printout quality cannot be satisfactory for the market, from which demands for maintenance of a certain homogeneous and acceptable level of printout quality probably will be put forth as essential requisites for the efficacy and applicability of these devices. By analyzing the state of the art through the above documents and in view of the discussed problem, a need of providing a means for ensuring enhanced and homogeneous quality-printing emerges, which should be accomplished preferably without interfering with the structural smallness of the hand-held printing devices as of current composition.